System and method for delay scheduling

ABSTRACT

A method includes determining a first subframe on which to transmit a first downlink control information (DCI) message and determining a second subframe on which to transmit a first information, where the first information is scheduled to be transmitted on the second subframe in accordance with scheduling information indicated in the first DCI message. The method also includes determining a delay between the first subframe and the second subframe and transmitting, by a communications controller to a user equipment (UE), the second subframe in accordance with the delay.

This application is a continuation of U.S. patent application Ser. No.13/899,251, filed May 21, 2013, entitled “System and Method for DelayScheduling,” which claims the benefit of U.S. Provisional ApplicationSer. No. 61/650,339 filed on May 22, 2012, and entitled “System andMethod for Delay Scheduling,” which applications are hereby incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a system and method for wirelesscommunications, and, in particular, to a system and method for delayscheduling.

BACKGROUND

In the Third Generation Partnership Project (3GPP) Long Term Evolution(LTE) Release-10 technical standards, transmissions from acommunications controller to user equipments (UEs) include both datachannels and control channels. LTE is a standard for wirelesscommunication of high speed data for mobile phones and data terminals.Compared to Global System for Mobile Communications (GSM) Enhanced DataRates for GSM Evolution (EDGE) and Universal Mobile TelecommunicationsSystem (UMTS) High Speed Packet Access (HSPA) network technologies, LTEincreases the capacity and speed of a network by using a different radiointerface along with core network improvements.

In LTE Release-10, the carrier bandwidth is one of six possible values(1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz). The frequencydimension contains subcarriers that may be 15 kHz apart. The timedimension of the system uses symbols, slots, subframes, and frames. Inan example, the slots are 0.5 ms in duration. The subframes may containtwo slots and be 1 ms in duration, while the frames may contain tensubframes and be 10 ms in duration. There are seven symbols in a slotwhen a normal cyclic prefix (CP) is used. When an extended CP is used,there are six symbols per slot. The subframes are numbered from 0 to 9.

SUMMARY

An embodiment method includes determining a first subframe on which totransmit a first downlink control information (DCI) message anddetermining a second subframe on which to transmit a first information,where the first information is scheduled to be transmitted on the secondsubframe in accordance with scheduling information indicated in thefirst DCI message. The method also includes determining a delay betweenthe first subframe and the second subframe and transmitting, by acommunications controller to a user equipment (UE), the second subframein accordance with the delay.

An embodiment method includes receiving, by a user equipment (UE) from acommunications controller, symbols of a first subframe including adownlink control information (DCI) message and receiving, by the UE fromthe communications controller, symbols of a second subframe inaccordance with a delay, where the symbols of the second subframeinclude information, and where the DCI message indicates scheduling ofthe information. The method also includes obtaining the delay.

An embodiment communications controller includes a processor and anon-transitory computer readable storage medium storing programming forexecution by the processor. The programming includes instructions todetermine a first subframe on which to transmit a first downlink controlinformation (DCI) message and determine a second subframe on which totransmit a first information, where the first information is scheduledto be transmitted on the second subframe in accordance with schedulinginformation indicated in the first DCI message. The programming alsoincludes instructions to determine a delay between the first subframeand the second subframe and transmit, to a user equipment (UE), thesecond subframe in accordance with the delay.

An embodiment user equipment (UE) includes a processor and anon-transitory computer readable storage medium storing programming forexecution by the processor. The programming includes instructions toreceive, from a communications controller, symbols of a first subframeincluding a downlink control information (DCI) message and receive, fromthe communications controller, symbols of a second subframe inaccordance with a delay, where the symbols of the second subframeinclude information, and where the DCI message indicates scheduling ofthe information. The programming also includes instructions to obtainthe delay.

The foregoing has outlined rather broadly the features of an embodimentof the present invention in order that the detailed description of theinvention that follows may be better understood. Additional features andadvantages of embodiments of the invention will be describedhereinafter, which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiments disclosed may be readily utilized as a basisfor modifying or designing other structures or processes for carryingout the same purposes of the present invention. It should also berealized by those skilled in the art that such equivalent constructionsdo not depart from the spirit and scope of the invention as set forth inthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates an embodiment system for delay scheduling;

FIG. 2 illustrates a downlink subframe;

FIG. 3 illustrates subframe numbering for frequency division duplexing;

FIG. 4 illustrates subframe numbering for time division duplexing;

FIG. 5 illustrates two consecutive subframes;

FIG. 6 illustrates an embodiment method of delay scheduling;

FIG. 7 illustrates the use of an offset value in a downlink controlinformation (DCI) message;

FIG. 8 illustrates the use of an offset value in a DCI message;

FIG. 9 illustrates another embodiment method of delay scheduling;

FIG. 10 illustrates an embodiment method of transmitting commonmessages;

FIG. 11 illustrates an embodiment method of receiving common messages;and

FIG. 12 illustrates a block diagram of an embodiment of ageneral-purpose computer system.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the embodiments andare not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

It should be understood at the outset that although an illustrativeimplementation of one or more embodiments are provided below, thedisclosed systems and/or methods may be implemented using any number oftechniques, whether currently known or not. The disclosure should in noway be limited to the illustrative implementations, drawings, andtechniques illustrated below, including the exemplary designs andimplementations illustrated and described herein, but may be modifiedwithin the scope of the appended claims along with their full scope ofequivalents.

FIG. 1 illustrates system 100 for delay scheduling. System 100 includescommunications controller 102, which may be referred to as an enhancednode B (eNB) or a base station. Coupled to communications controller 102are user equipment (UE) 104, UE 106, and UE 108. In an example, UEs 104,106, and 108 are mobile devices. Three UEs are pictured, but more orfewer UEs may be coupled to a single communications controller. One ormore of UEs 104, 106, and 108 can be machine type communications (MTC)devices. The MTC device may be a wireless sensor, where the sensor takessome measurements. The sensor then conveys the information about themeasurements using a wireless protocol. For instance, smart metering canbe implemented using MTC technology. Other UEs are non-MTC devices, forexample cell phones or other traditional devices.

MTC devices have a subset of features of non-MTC devices. For example,MTC devices may support a reduced bandwidth. In an example, a non-MTCdevice supports a bandwidth of up to 20 MHz, while an MTC device maysupport a bandwidth of 5 MHz or less. MTC devices are generally lessexpensive than non-MTC devices. One example of a less expensive MTCdevice may have a restricted payload size. Also, in another example, MTCdevices may use only one receive antenna. In some applications, MTCdevices are used in remote areas, such as basements, and need anadditional 20 dB in link budget to have an equivalent coverage to thatof non-MTC devices.

A system containing both MTC devices and non-MTC devices, such as system100, provides compatibility to both MTC devices and non-MTC devices. Forexample, a physical downlink control channel (PDCCH) intended fornon-MTC devices may be transmitted at the 20 MHz bandwidth. A physicalcontrol format indicator channel (PCFICH), which may also indicate thewidth of a control region, may be transmitted across the 20 MHzbandwidth. The width can be represented by a number of OFDM symbols. AnMTC device operating at a lower bandwidth receives portions of the PDCCHand PCFICH, but not the entire PDCCH and PCFICH. When an MTC devicecannot receive the entire PCFICH, it may not know the duration of thecontrol region.

In LTE or enhanced LTE systems, resource scheduling is implemented in atransmission time interval (TTI). For example, the TTI may betransmitted with a 1 ms time interval. UE 104 initially receives thedownlink control information (DCI) message in a physical downlinkcontrol channel (PDCCH). The DCI message may indicate the schedulinginformation for downlink data in a physical downlink shared channel(PDSCH) in the current subframe. For example, the DCI message includesresource allocation (RA), the modulation and coding scheme (MCS), andadditional information. Also, the DCI message may indicate schedulinginformation for uplink data in the physical uplink shared channel(PUSCH) in a future subframe. In one example, the PDCCH spans the entirecarrier bandwidth in the frequency domain, and occupies between one andfour orthogonal frequency division multiplexing (OFDM) symbols in thetime domain. When the carrier bandwidth is 3 MHz, 5 MHz, 10 MHz, 15 MHz,or 20 MHz, up to three OFDM symbols are used for the PDCCH. On the otherhand, when a 1.4 MHz carrier bandwidth is used, the PDCCH is transmittedusing between two and four OFDM symbols. A master information block(MIB) is transmitted on the center six resource block (RB) pairs. Then,subsequent access by UE 104 uses configuration information, such as thebandwidth, from the MIB. UE 104 may be scheduled to receive or transmitdata on one or more physical resource block (PRB) pairs. In an example,the PRB pair occupies several OFDM symbols in the time domain and fromtwelve subcarriers to the entire bandwidth in the frequency domain. Inone example, the number of symbols in a PRB pair is equal to the numberof symbols in the data region. In an MTC device, a subset of the entiredownlink PRB space may be examined in each subframe.

Symbols corresponding to a downlink subframe may be transmitted fromcommunications controller 102 to UE 104. FIG. 2 illustrates downlinkframe 110, which contains control region 112 and data region 114. The xaxis illustrates the time domain, and the y axis illustrates thefrequency domain. Control region 112 may contain a PDCCH, a physicalcontrol format indicator channel (PCFICH), a physical hybrid automaticrequest (HARQ) indicator channel (PHICH), and other signals, such ascommon reference symbols. In general control region 112 may containzero, one, or more than one PDCCH. Control region 112 spans the entirebandwidth. Data region 114 may contain a PDSCH and other channels andsignals. In general, data region 114 may contain zero, one, or more thanone PDSCH.

An LTE system may use frequency division duplexing (FDD) or timedivision duplexing (TDD). TDD is an application of time-divisionmultiplexing to separate uplink and downlink signals in time, possiblywith a guard period situated in the time domain between the uplink anddownlink signaling. In FDD, the uplink and downlink signals are atdifferent carrier frequencies.

FIG. 3 illustrates downlink (DL) frame 122 and uplink (UL) frame 124 inan FDD system. Downlink frame 122 includes subframes 210-219, whileuplink frame 124 contains subframes 220-229. The carrier frequency fordownlink frame 122 is different from the carrier frequency for uplinkframe 124. In an example, subframe 210 contains the PDCCH withscheduling information for the PDSCH in subframe 210. The PDCCH insubframe 210 also contains scheduling information for the physicaluplink shared channel (PUSCH) in subframe 224. In FDD, the onset ofsubframe 21 x and subframe 22 x happen at the same time, where x is aninteger between 0 and 9.

FIG. 4 illustrates frame 132 for use in a TDD system. In frame 132,subframes 310 and 315 are downlink subframes, while subframes 311 and316 are special subframes. Special subframe contains a downlink pilottime slot (DwPTS), a guard period (GP), and an uplink pilot time slot(UpPTS). Subframes 312, 313, 314, 317, 318, and 319 are uplinksubframes.

Delay scheduling may be used by the communication controller to receiveor transmit information in later subframes. Delay scheduling facilitatesthe coexistence of MTC devices in a network that also supports non-MTCdevices. In delay scheduling, delay values may be fixed orsemi-statically changed. In one example, different delay values are usedfor different device types. For example, one delay value is used for MTCdevices, while another delay value is used for non-MTC devices. Forbackwards compatibility, the delay value for certain non-MTC devices maybe implicitly 0. In another example, one MTC device has a first delayvalue while another MTC device has a second delay value. With differentdelay values, separate common messages are sent to the MTC devices andthe non-MTC devices. When delay scheduling is used, the HARQ timing maybe adjusted, and resources for a HARQ response are reserved. When halfduplex FDD (HD-FDD) is used, fixed or semi-statically configurableuplink and downlink configurations may be defined as in TDD.Alternatively, an uplink or downlink transmission may be droppeddepending on its priority when a conflict appears. Delay scheduling mayenable MTC devices to operate with an additional 20 dB of margin. Also,delay scheduling may allow MTC devices with small bandwidths to switchfrequency subcarriers to receive data with the benefit of frequencyselective scheduling.

If a UE, such as an MTC device, can obtain scheduling information beforebuffering of downlink transmissions, the UE may buffer only thescheduled physical resources, not the entire bandwidth of data. The sizeof buffer may be reduced, reducing the cost of the MTC device. Alsosystem performance may be improved by frequency selective scheduling.

Another control channel in LTE is the enhanced PDCCH (ePDCCH). Like thePDCCH, the ePDCCH carries both uplink grants and downlink assignments.However, unlike the PDCCH, the ePDCCH uses a UE specific demodulationreference signal (DMRS).

The ePDCCH may have a user specific search space, which may include aset of enhanced CCEs (eCCEs), and may be defined in terms of eCCEs orRBs. The ePDCCH spans only a narrow band of frequency resources, butfrequency multiplexes with the PDSCH. FIG. 5 illustrates an example forfrequency allocation in an MTC device for two consecutive subframes,subframe 142 and subframe 144. Subframe 142 contains control region 146and data region 148, which contains PDSCH 150. Control region 146 maycontain a DCI message for non-MTC devices. Data region 148 may carry theePDCCH for the MTC device in subframe 142. Similarly, subframe 144contains control region 152 and data region 154, which contains PDSCH156. Like data region 148, data region 154 may carry the ePDCCH for theMTC device in subframe 144. In an example, the ePDCCH in data region 148and the ePDCCH in data region 154 occupy different PRB pairs. The ePDCCHmay occupy all symbols of a subframe except for the control region.Because the ePDCCH occupies all symbols of data region 148, it isdesirable for devices to have the ability to decode the DCI message inthe ePDCCH very quickly or use delay scheduling to determine when thePDSCH associated with the ePDCCH can be received. Because the UEprocesses the ePDCCH first, it must receive the symbols of the dataregion for that subframe initially.

There are potential issues using the ePDCCH. With non-MTC devices, oncea DCI containing scheduling information for a PDSCH is identified, thenon-MTC device can then process the resources associated with thatPDSCH, because the symbols or subcarriers bearing those resources werestored in a buffer. The buffer enables non-MTC devices to process PRBscarrying the associated PDSCH in the same subframe as the ePDCCH.Processing both the ePDCCH and the associated PDSCH of the same subframeimplies that the size of the buffer is large. An MTC device may processthe ePDCCH and associated PDSCH in the same subframe if certainconditions hold. Such conditions include the size of the resourcescorresponding to the number of PRB pairs for the ePDCCH, the associatedPDSCH, and that the gap between the ePDCCH and PDSCH is not greater thanthe size of the buffer. Also, the ePDCCH and associated PDSCH shouldoccupy the PRB pairs that are within the bandwidth of the MTC device.However, to ensure that MTC devices are not expensive, the size of thebuffer should be as small as possible. For an MTC device, acommunications controller might follow these exemplary conditions. Thereis no guarantee that the communications controller can satisfy theseconditions while meeting the LTE requirements for other UEs in thesystem. An alternate approach for scheduling for ePDCCH and theassociated PDSCH is needed for MTC devices.

Due to location of the ePDCCH in subframe k, a UE may store symbols ofthe next subframe (k+1) as it is processing ePDCCH. For an MTC devicethat processes a subset of the PRB pairs of the possible PRB pairs inthe system in each subframe, the MTC device may not know beforehandwhich subset of PRB pairs to store in subframe (k+1) until it finishedprocessing the ePDCCH in subframe k. Furthermore, a communicationscontroller may be unable to transmit the PDSCH in subframe k+1 using thesame bandwidth as the ePDCCH in subframe k. For example, in an overall20 MHz downlink transmission, an MTC device may be able to use only 1.4MHz (6 PRB pairs such as PRB pairs 6 to 11). In subframe k, the ePDCCHmay be transmitted using some PRB pairs between PRB pairs 6 and 11,while the associated PDSCH in subframe k+1 is located in a region of PRBpairs 12-17. The MTC device may be unable to change the frequency bandcorresponding to the different set of PRB pairs for what it capturingwithout additional delay.

Another benefit to using the ePDCCH is power savings. With delayscheduling, the MTC device can skip processing future subframes if thereis no scheduled PDSCH. Furthermore, if there are rules, such as that theePDCCH and PDSCH cannot be transmitted in the same subframe to a givenMTC device, further power savings may be achieved.

In an embodiment, the ePDCCH and the scheduled PDSCH are in differentsubframes. When delay scheduling is used, an MTC device buffers only thescheduled data, not the entire bandwidth of data. Thus, the MTC devicemay be implemented at a lower cost compared to a non-MTC device due to areduced buffer size or relaxed operation speed.

FIG. 6 illustrates flowchart 160 for a method of delay scheduling. Thismethod is performed by communications controller 102. Initially, in step162, communications controller 102 determines whether it has informationfor an MTC device. The information may be data information, controlinformation, or both. This information may be transmitted on the PDSCH.When communications controller 102 does not have information for an MTCdevice, the method ends in step 161.

When there is information for an MTC device, communications controller102 proceeds to step 164, where it determines on which subframe totransmit the DCI message. Communications controller 102 decides whetherto transmit the DCI message on the PDCCH or ePDCCH. The decision may bebased on the capabilities of the device. Also, communications controller102 decides on which resources to place the DCI message. When the PDCCHis used, the resources may be control channel elements (CCEs) and theaggregation level. On the other hand, when the ePDCCH is used, theresources used may be the aggregation level, eCCEs, and one or more PRBpairs. Additionally, communications controller 102 decides what type ofDCI message to transmit, and on which PRB pair(s) to transmit the PDSCH.In one example, the DCI message contains a field or offset for whichlater subframe or subframes contain the downlink data or are granted foruplink transmission.

After determining on which subframe to transmit the DCI message,communications control 102 transmits the subframe (i.e., the OFDMsymbols of the subframe) with the DCI message to UE 104. Information,such as the PDSCH, is also transmitted to UE 104 in a separate subframein step 166.

Finally, in step 170, communications controller 102 receives anacknowledgement associated with the transmission of information (e.g.,PDSCH) to UE 104. An acknowledgement in step 170 can represent apositive acknowledgement (ACK), implying that the reception ofinformation was correct, or a negative acknowledgment (NACK), implyingthat the reception of information was incorrect. Assuming that the PDSCHis sent in the kth subframe, for an FDD system, communicationscontroller 102 receives the acknowledgement in the (k+4)th subframe. Onthe other hand, in a TDD system, communications controller 102 receivesthe acknowledgement, for example in the first uplink subframe that is inor after the (k+4)th subframe. In LTE Release-10, the resources for theacknowledgement are based on the index of the CCE for DCIs send on thePDCCH, and the transmission of the acknowledgement by an UE is based onthe reception of the PDCCH. When it is sent on the ePDCCH, a procedurebased on configuration parameters for the ePDCCH is used to determinethe resources for the acknowledgement. With delay scheduling, thetransmission of the acknowledgement can be based on the when thesubframe containing the PDSCH was received. The transmission of theacknowledgement may also be based on when the PDCCH/ePDCCH was receivedand the delay value.

FIG. 7 illustrates frame 180, which may be used for delay scheduling.Frame 180 contains consecutive subframes 182, 184, and 186. The DCI insubframe 182 may convey a bit field, for example three bits, thatindicates which subframes are scheduled for downlink transmission. Thebit field could be an index of a table of delay values. The bit fieldcan also represent the delay value directly. For example, if the DCI istransmitted on subframe 182, the kth subframe, a delay value of 0indicates that the scheduled PDSCH is in the kth subframe. However, adelay value of 1 indicates that the PDSCH is transmitted in the (k+1)thsubframe (subframe 184), and a delay value of 2 indicates that the PDSCHis transmitted in the (k+2)th subframe (subframe 186). For MTC devices,when the DCI is transmitted in the PDCCH in subframe 182, the delayvalue of 0 may be disallowed, because subframe 182 cannot be used forits PDSCH for that MTC device. When the DCI is transmitted in the ePDCCHof subframe 182 for an MTC device, the values of 0 and 1 are disallowed,because, for that MTC device, its PDSCH cannot be transmitted onsubframes 182 and 184.

For MTC devices, one reason for the delay value restrictions for thePDCCH and the associated PDSCH can be buffer size limitations. Insubframe k, the MTC device can receive the symbols corresponding to thecontrol region. The MTC device can then process both the common searchspace and UE specific search space of the PDCCH to find a DCI directedtowards the MTC device. With delay scheduling, the MTC device candetermine which data regions to capture in a future subframe. Insubframe k, the MTC device stores all the resource elements of thesymbols for the control region. Unless the width of the control regionis known beforehand (e.g. via higher layer signaling or through astandards specifications), the MTC device may have to store symbolsbased on the maximum size of the control region. In one instance, for a20 MHz system, there are 1200 resource elements per symbol, and amaximum size of the control region is 3 symbols. The MTC device may haveto store 3×1200=3600 resource elements. If the communications controllerindicates, with delay scheduling, that the PDSCH associated with thePDCCH is in subframe k+1, and the number of PRBs pairs used that PDSCHis 6 (corresponding to 1.4 MHz), the MTC device may store 72resources/symbol×14 symbols=1008 resource elements of subframe k+1.Without delay scheduling, a device may store 1200 resource elements persymbol×14 symbols/per subframe=16,800 resource elements. Since the PDCCHis located in the first few symbols of subframe k, the MTC device canfinish processing the PDCCH in subframe k and still prepare forcapturing a narrowband PDSCH in subframe k+1.

FIG. 8 illustrates an example of a DCI offset, which can be the label ofthe bit field in FIG. 7. DCI message 192 contains offset 194 andoriginal DCI 196. Offset 194 is placed in original DCI 196, for exampleby prepending. Alternatively, offset 194 is placed at the end oforiginal DCI 196. The offset for PDSCH transmission for MTC devices maybe a subset of a range when the same DCI format is also used for non-MTCdevices. Also, when the DCI message is in subframe k, there may beindicators or mappings indicating the width of the control region ofsubframe k+d, where d is determined by DCI offset 194 in DCI message192. Alternatively, there may be indicators, mappings, and/or higherlayer signaling to indicate the starting symbol of the associated PDSCHin subframe k+d.

FIG. 9 illustrates flowchart 230 for a method of delay schedulingperformed by UE 104. In one example, UE 104 is an MTC device. In anotherexample, UE 104 is a non-MTC device. Initially, in step 232, UE 104examines on which subframe it will receive a DCI message. UE 104 maysearch for a DCI on every subframe, in which case step 232 is bypassed.During discontinuous reception (DRX), UE 104 examines certain subframes.For MTC devices, there may be configurable periods where the devicelooks for the DCI. When UE 104 only receives the DCI message on theePDCCH, UE 104 determines which PRB pair contains the ePDCCH.

Then, in step 234, UE 104 receives the symbols of the subframecontaining the DCI message from communications controller 102. This isdone, for example, by searching the appropriate search spaces of thePDCCH or ePDCCH for the locations of the PDCCH or ePDCCH carrying themodulated DCI. Upon finding the DCI message, UE 104 processes the DCImessage to determine its contents. UE 104 also receives information fromcommunications controller 102, for example in the same subframe or asubsequent or future subframe. The information conveyed in the PDSCH maybe data information, control information (such as higher layersignaling), or both. UE 104 receives the PDSCH based on the processedDCI message. The delay value for receiving the PDSCH may be based on thecontents of the DCI message, the broadcast information, or specificationrules. Rules in the specification may indicate the timing between theDCI message and the associated PDSCH. Also, UE 104 may obtain a delayvalue, for example from broadcast information, such as a physicalbroadcast channel PBCH or an enhanced PBCH (ePBCH). In another example,UE 104 obtains a delay value by receiving the delay value in a highlayer radio resource control (RRC) signal, such as the systeminformation (SI). In an additional example, UE 104 knows the delayvalue.

Then, in step 238, UE 104 transmits an acknowledgement message tocommunications controller 102. In an example, communications controller102 reserves a physical uplink control channel (PUCCH) foracknowledgment from UE 104 to avoid PUCCH resource conflicts between MTCdevices and non-MTC devices.

In an embodiment, UE 104 operates in HD-FDD mode. In HD-FDD mode, theacknowledgement is transmitted by UE 104 after a fixed delay fromreceiving the PDSCH. For example, UE 104 transmits the PUSCH in the(n+4)th subframe after detecting the uplink grant in the nth subframe.To simplify the scheduler for communications controller 102, when aconflict between uplink and downlink transmission appears, either theuplink or downlink transmission is dropped. For example the transmissionwith the lower priority is dropped.

In one example, delay scheduling is used for MTC devices, but not fornon-MTC devices. For example, non-MTC devices may be scheduled byanother method, such as using a PDCCH or ePDCCH to schedule the PDSCH inthe current subframe. Alternatively, delay scheduling is used for bothMTC devices and non-MTC devices. When delay scheduling is only used forMTC devices, the delay may be a fixed value d. Communications controller102 transmits the PDCCH or ePDCCH in the nth subframe to schedule thePDSCH in the (n+d)th subframe. For example, d may be 2, 3, or anothervalue. In one embodiment, the value of d is written into thespecification. Both communications controller 102 and UE 104 know thevalue of d. A benefit of an embodiment is how delay scheduling mayfacilitate an extra 20 dB of coverage for MTC devices. In one example,more than one subframe, for example 200 subframes, may be used totransmit the same DCI to a particular MTC device. After decoding theDCI, the MTC device may begin receiving the PDSCH, possibly in multiplesubframes after obtaining the delay value.

In another example where delay scheduling is used only for MTC devices,the delay value is transmitted in the physical broadcast channel (PBCH)or enhanced PBCH (ePBCH). In this example, communications controller 102or another part of the network sets the delay value. UE 104 then obtainsthe delay value, for example by extracting it, from the PBCH or ePBCH.

When delay scheduling is used for both MTC devices and non-MTC devices,there may be two or more delay values. For example, MTC devices use onefixed delay value to receive the system information block 1 (SIB1)message. Non-MTC devices receive both the DCI message and the SIB1 onsubframe 5, while MTC devices cannot receive the DCI and SIB1 in thesame subframe. The MTC device then receives another delay value afterprocessing the SIB1 message. The second delay value may be configured bythe network, and may override the first value. For example, the firstdelay indicates that the SIB1 message is transmitted in subframe 5.However, the corresponding DCI message (carried in either the PDCCH orePDCCH for the SIB1 message) is transmitted at a fixed earlier delay,such as in subframe 3. In another example, the PDCCH or ePDCCH for theSIB1 message is transmitted in subframe 5, while the SIB1 message forthe MTC device is transmitted in a later subframe.

In one embodiment, the delay value may be signaled by the DCI message.There can be a field in the DCI message to indicate which subframe is orsubframes are scheduled for the device to transmit data on for uplink orto receive data on for downlink. In one example, the DCI message has onevalue when scheduling SIB messages on the PDSCH and another value whenscheduling other information on the PDSCH. In this example, non-MTCdevices may use an offset for the common messages when a single SIBmessage is used. For backwards compatibility, the DCI message may nothave a delay field for non-MTC devices.

Delay scheduling may also be used in TDD. However, in TDD, because theremay be uplink subframes interspersed between downlink subframes, someuplink subframes may be skipped over before transmitting the PDSCH in adownlink subframe using delay scheduling. Because communicationscontroller 102 has no knowledge of the UE device type until the randomaccess channel (RACH) process, communications controller 102 assumesthat both MTC devices and non-MTC devices exist in the cell. In oneexample, communications controller 102 transmits a single DCI scrambledby system information radio network system information (SI-RNTI), pagingRNTI (P-RNTI), or random access response RNTI (RAR-RNTI). However,communications controller 102 transmits two PDSCH in different subframesbased on the single DCI. UE 104 knows how to interpret the delay of thePDSCH based on its capability (such as a category 1, category 2, andpossibly category 0 device), and the subframe in which the DCI wasreceived. All fields in the DCI messages are common for these two PDSCH.For non-MTC devices, the PDSCH is received on the same subframe as thePDCCH or ePDCCH with an implicit delay of zero. For MTC devices, thereis a delay between receiving the PDCCH or ePDCCH and the PDSCH.

In another embodiment, two DCI messages are used to schedule a commonbroadcast PDSCH (e.g. SIB1). One DCI message is used for non-MTCdevices, and the other DCI message is used for MTC devices.

In an embodiment, common messages are transmitted in known PRBs withfixed MCS and locations. Thus, no delay is needed. This information maybe conveyed in other RRC messages.

FIG. 10 illustrates flowchart 240 for a method of transmitting commonmessages by communications controller 102. Initially, in step 242,communications controller 102 determines whether it supports multipletypes of devices. For example, communications controller 102 may supportboth MTC devices and non-MTC devices. In one example, communicationscontroller 102 is required to support multiple types of device. Whencommunications controller 102 does not support multiple types ofdevices, the method goes to step 243 and ends.

When communications controller 102 supports multiple types of devices,whether duplicate or separate common messages will be transmitted todifferent device types may be specified, for example in a standard. Forexample, MTC devices and non-MTC devices may not be capable of receivingcommon messages in the same subframe. Examples of common messagesinclude system information (SI), paging, and RAR messages. Whencommunications controller 102 supports multiple types of devices, it mayencapsulate separate common messages for different device types. On theother hand, communications controller 102 may duplicate the same commonmessage for the different types of devices.

Next, in step 245, communications controller 102 determines the DCImessages and the contents for the common messages. When one DCI messageis used for the common messages, communications controller 102 maytransmit duplicate or separate common messages in different subframes.In one example, the same message is duplicated and transmitted indifferent subframes. In another example, separate messages aretransmitted. One message is targeted at non-MTC devices in the samesubframe as the DCI, and a similar message, possibly with slightlydifferent parameters or fields, is targeted at MTC devices in a futuresubframe. On the other hand, when two DCI messages are used, one foreach type of device, the DCI messages are separately scrambled. Forexample, the DCI message for non-MTC devices is scrambled by SI-RNTI,P-RNTI, or RAR-RNTI. On the other hand, the DCI message for MTC devicescan be scrambled by new RNTIs, such as multicast channel (MCH)scheduling information RNTI (MSI-RNTI), multiple P-RNTI (MP-RNTI), ormultiple RAR RNTI (MRAR-RNTI). In scrambling the DCI messages, thecyclic redundancy check (CRC) code is computed to produce a paritysequence. Then, the parity sequence is added to the RNTI value using abitwise exclusive-or operation. Finally, this value is appended to theoriginal DCI message. An example of a modulated DCI is a DCI messagethat is scrambled, encoded, interleaved, rate matched, and mapped in asequence of constellation points, such as quadrature phase shift keying(QPSK) points. In another embodiment, the DCI message length isdifferent for MTC devices and non-MTC devices. For example, a DCI format1A message may be 27 bits for non-MTC devices, but 31 bits for MTCdevices. The difference in size of the messages can be due to a fieldrepresenting the delay value. In this example, the same scrambling valueis used for both messages. In an example, communications controller 102also decides whether to transmit the DCI message within the PDCCH or theePDCCH. Communications controller 102 may determine which resources toplace the modulated DCI message on or determine the type of DCI messageto transmit. Additionally, communications controller 102 may determinewhich PRB pair(s) to transmit the PDSCH on.

After determining the DCI messages, communications controller 102, instep 246, determines which subframe to transmit the PDCCH or ePDCCH onfor the common message or messages. For example, when a SIB1 message isused, the SIB1 is transmitted on subframe 5. The PDCCH or ePDCCH is alsotransmitted in subframe 5 for non-MTC devices, with no delay (animplicit delay value of 0). On the other hand, for MTC devices, thePDCCH or ePDCCH is transmitted earlier with a time advance. For example,the PDCCH or ePDCCH is transmitted on subframe 3. Alternatively, thePDCCH or ePDCCH is also transmitted on subframe 5 for MTC devices, andthe duplicated SIB1 or separate SIB1 is transmitted in a later subframefor MTC devices.

Finally, in step 247, communications controller 102 transmits the commonmessages to UE 104. This is done in accordance with the subframeconveying the PDCCH or ePDCCH.

FIG. 11 illustrates flowchart 250 for a method of receiving commonmessages by UE 104 when multiple types of devices coexist in a cell. UE104 may be an MTC device or a non-MTC device. Initially, in step 252, UE104 receives a common message from communications controller 102.

After receiving the common message, UE 104 determines whether themessage is a common message specific to the device type of UE 104 or acommon message shared with other device types, in step 254. In oneexample, whether common messages are device specific or shared is asystem configuration, which for example is transmitted on the PBCH.

Then, in step 256, UE 104 determines the number of DCI messagestransmitted on the common search space. There may be zero, one, or moreDCI messages transmitted on the common search space. When there is a DCImessage, different device types may interpret the DCI messagedifferently. For example, the resource assignment (RA) field in the DCIis distributed for non-MTC devices but concentrated for MTC devices.When there are two DCI messages, non-MTC devices may receive one DCImessage scrambled by SI-RNTI, P-RNTI, or RAR-RNTI, while MTC devicesreceive the other DCI message scrambled with new RNTIs, such asMSI-RNTI, MP-RNTI, or MRAR-RNTI.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

What is claimed is:
 1. A method comprising: determining a first subframeon which to transmit a first downlink control information (DCI) message;determining a second subframe on which to transmit a first information,wherein the first information is scheduled to be transmitted on thesecond subframe in accordance with scheduling information indicated inthe first DCI message; determining a delay between the first subframeand the second subframe; and transmitting, by a communicationscontroller to a user equipment (UE), the second subframe in accordancewith the delay.
 2. The method of claim 1, wherein the delay is fixed. 3.The method of claim 1, wherein the delay is zero.
 4. The method of claim1, wherein the second subframe is a subframe of a physical downlinkshared channel (PDSCH).
 5. The method of claim 1, wherein determiningthe delay between the first subframe and the second subframe comprisesdetermining the delay between the first subframe and the second subframein accordance with a capability of the UE.
 6. The method of claim 1,wherein determining the delay between the first subframe and the secondsubframe comprises determining the delay in accordance with the firstinformation.
 7. The method of claim 1, wherein the first DCI messagecomprises a field indicating the delay.
 8. The method of claim 1,further comprising transmitting, by the communications controller to theUE, the delay on higher layer signaling.
 9. The method of claim 1,wherein the second subframe further comprises a second DCI message,wherein the second DCI message indicates scheduling of the firstinformation.
 10. The method of claim 9, wherein the first DCI messagecorresponds to a first device category of the UE and the second DCImessage corresponds to a second device category of the UE.
 11. Themethod of claim 1, wherein the first subframe comprises a secondinformation, wherein the first DCI message indicates scheduling of thesecond information.
 12. The method of claim 1, further comprisingdetermining whether the communications controller supports differentdevice categories.
 13. A method comprising: receiving, by a userequipment (UE) from a communications controller, symbols of a firstsubframe comprising a downlink control information (DCI) message;receiving, by the UE from the communications controller, symbols of asecond subframe in accordance with a delay, wherein the symbols of thesecond subframe comprise information, and wherein the DCI messageindicates scheduling of the information; and obtaining the delay. 14.The method of claim 13, wherein obtaining the delay comprises receiving,by the UE from the communications controller, the delay.
 15. The methodof claim 13, wherein obtaining the delay comprises obtaining the delayby a higher layer signaling.
 16. The method of claim 13, furthercomprising transmitting, by the UE to the communications controller, anacknowledgment delay after receiving the symbols in accordance with theinformation and the delay.
 17. The method of claim 16, wherein theacknowledgment delay is at least four subframes.
 18. The method of claim13, wherein receiving the symbols of the second subframes comprisesreceiving the symbols of the second subframe in accordance with acapability of the UE.
 19. A communications controller comprising: aprocessor; and a non-transitory computer readable storage medium storingprogramming for execution by the processor, the programming includinginstructions to determine a first subframe on which to transmit a firstdownlink control information (DCI) message, determine a second subframeon which to transmit a first information, wherein the first informationis scheduled to be transmitted on the second subframe in accordance withscheduling information indicated in the first DCI message, determine adelay between the first subframe and the second subframe, and transmit,to a user equipment (UE), the second subframe in accordance with thedelay.
 20. A user equipment (UE) comprising: a processor; and anon-transitory computer readable storage medium storing programming forexecution by the processor, the programming including instructions toreceive, from a communications controller, symbols of a first subframecomprising a downlink control information (DCI) message, receive, fromthe communications controller, symbols of a second subframe inaccordance with a delay, wherein the symbols of the second subframecomprise information, and wherein the DCI message indicates schedulingof the information, and obtain the delay.